When speech/sound signals are transmitted in a packet communication system represented by Internet communication, mobile communication system and so on, compression/coding techniques are often used to improve the transmission efficiency of speech/sound signals. Furthermore, in the recent years, while speech/sound signals are being encoded simply at low bit rates, there is a growing demand for techniques for encoding speech/sound signals of wider band.
To meet this demand, studies are underway to develop various techniques for encoding wideband speech/sound signals without drastically increasing the amount of encoded information. For example, patent document 1 discloses a technique of generating features of the high frequency band region in the spectral data obtained by converting an input acoustic signal of a certain period, as side information, and outputting this information together with encoded information of the low band region. To be more specific, the spectral data of the high frequency band region is divided into a plurality of groups, and, in each group, regards the spectrum of the low band region that is the most similar to the spectrum of the group, as the side information mentioned above.
Furthermore, patent document 2 discloses a technique of dividing the high band signal into a plurality of subbands, deciding, per subband, the degree of similarity between the signal of each subband and the low band signal, and changing the configurations of side information (i.e. the amplitude parameter of the subband, position parameter of a similar low band signal, residual signal parameter between the high band the and the low band) according to the decision result.
Patent Document 1: Japanese Patent Application Laid-Open No. 2003-140692
Patent Document 2: Japanese Patent Application Laid-Open No. 2004-004530